I am 63 years old and have noticed very mild discomfort in the sternum area for approximately the last 10 days. I do lift weights but have not noticed anything unusual during the routine e.g. no muscle pull. I also play quite a bit of racquetball and today while playing there was discomfort in the sternum area with some difficulty in breathing. Currently it feels somewhat like an overexercised muscle. There are currently no additional symptoms. There is ,however, a fair degree of family related stress at this time. What should be my next step.